Krypton and xenon are undergoing increasing demand in a number of applications. Krypton is being widely used in high quality lighting including long-life light bulbs and automotive lamps. Xenon is being used for medical applications including special x-ray equipment. Both of these gases are commonly used in many laboratory and research applications.
The principle source of krypton and xenon is the atmosphere. Atmospheric air contains about 1.1 ppm (parts per million) of krypton and about 0.08 ppm of xenon. Generally, krypton and xenon are recovered from the air in conjunction with a comprehensive air separation process which separates air into oxygen and nitrogen.
Due to the lower vapor pressure of krypton and xenon, these gases concentrate in the oxygen rather than in the nitrogen during the air separation. The concentration of the atmospheric krypton and xenon in the oxygen increases their concentration by a factor of five because oxygen comprises only about one-fifth of the atmospheric air. It is desirable to further concentrate the krypton and xenon so that they may be effectively recovered in a rare gas recovery facility.
Generally one wishes to produce gaseous oxygen from the air separation process. As described earlier, the krypton and xenon concentrate in the oxygen. Therefore, in order to produce both gaseous oxygen product, and a further concentration of krypton and xenon, one must pass the entire amount of gaseous oxygen through the concentrating process. A typical concentrating process involves a stripping column. Since the entire gaseous oxygen product must be passed through the stripping column, the stripping column must be relatively large. Furthermore, the oxygen passing through the stripping column is subject to pressure drop which adds to the costly compression if the oxygen product is desired at elevated pressure. This is costly from both a capital and operating cost standpoint.
Therefore it would be very desirable to have a krypton-xenon concentration process which produces gaseous oxygen but can employ a stripping column significantly smaller than heretofore considered necessary for conventional processes.
It is therefore an object of this invention to provide an improved process to produce a krypton-xenon concentrate.
It is another object of this invention to provide an improved process to produce a krypton-xenon concentrate while also producing a gaseous oxygen product substantially free of rare gases.
It is still another object of this invention to provide an improved process to produce a krypton-xenon concentrate and a gaseous oxygen product while employing a stripping column significantly smaller than employed by conventional processes.